In the field of scanning probe microscopy, small probes interact with systems under test to measure mechanical properties of the systems under test. For example, in atomic force microscopy, a small probe (typically sub-micrometer sized) is attached to the end of a cantilever. As the probe is scanned across the surface of a system under test, such as the membrane of a cell, surface irregularities impose a varying force on the probe, which, in turn, in a bending or deflection of the cantilever. An optical sensor senses the deflection of the cantilever based on light reflected from the cantilever and thereby determines changes in normal position of the probe as it is scanned across the surface of the system under test. The changes in normal position of the probe are used to map the surface of the system under test.
FIG. 1A illustrates a typical application of atomic force microscopy. In FIG. 1A, a probe 100 is attached to the end of cantilever 102 to map the surface 104 of a cell membrane. A laser, an optical sensor, and a computer (not shown) are used to map surface 104 as probe 100 causes deflections in cantilever 102. One problem with atomic force microscopy is illustrated in FIG. 1B. Atomic force microscopy requires a mechanical connection between probe 100 and the remainder of the system via cantilever 102. As a result, conventional atomic force microscopy is unsuitable for measuring mechanical properties of structures within enclosed regions, such as organelles within a cell membrane, or the other structures that are inaccessible for scanning with a mechanically attached probe.
One way to measure properties of structures inside of cells and other enclosed environments, is to mechanically decouple the probe from the remainder of the system. However, once the probe is mechanically decoupled from the remainder of the system, tracking and controlling movement of the probe become problematic. One known technique of applying force to a mechanically decoupled probe is referred to as “optical tweezers.” This technique requires high optical field intensities that interact strongly with many materials and may produce undesirable side effects on experiments in biological systems.
Magnetic techniques have also been developed for moving probes in two dimensions. However, methods and systems for three dimensional motion control and tracking of a free-floating particle, prior to the present invention, are not known to be developed. Such a motion control and tracking system would be particularly useful for measuring mechanical properties of living organisms in biological environments and in materials science. Accordingly, there exists a long felt need for methods and systems for three dimensional motion control and tracking of a mechanically unattached, free-floating probe.